Chiroptical properties of acridino-18-crown-6 ligands and their complexes with chiral and achiral protonated primary (aralkyl) amine guest molecules.

This paper reports CD spectroscopic studies on acridino-18-crown-6 ligands (R,R)-2 and 2a (see Figure 1), and their complexes with the enantiomers of alpha-(1-naphthyl)ethylamine hydrogenperchlorate (1-NEA), 1-phenylethylamine hydrogenperchlorate (PEA) and alpha-(2-naphthyl)ethylamine hydrogenperchlorate (2-NEA), and also with the achiral guests (1-naphthyl)methylamine hydrogenperchlorate (1-NMA), benzylamine hydrogenperchlorate (BA), methylamine hydrogenperchlorate (MA) and 1-methylnaphthalene (1-MN). The general feature of the CD spectra of complexes of (R,R)-2 with MA, BA, (R)- and (S)-PEA is the replacement of the oppositely signed B-1(b) doublet of the host by one positive band near 265 nm. The CD spectra of the heterochiral and homochiral complexes of phenazino and acridino hosts (R,R)-1, la, (R,R)-2 and 2a with (R)- and (S)-l-NEA and 1-NMA are governed by exciton interaction. Surprisingly, the heterochial [(R,R)/(S)] complexes of the structural isomeric 2-NEA gave rise to a positive couplet. in contrast to the negative couplet measured in the spectrum of the heterochiral [(R,R)/(S)] complexes of 1-NEA.